Device and method for operating volumetric expansion machines

ABSTRACT

The invention relates to a device comprising: an expansion machine for generating mechanical energy by expanding vapor of a working medium; a generator connected to a shaft of the expansion machine and used for generating electric energy from mechanical energy of the expansion machine; wherein the expansion machine and the generator form a structural unit with an exhaust vapor chamber between the expansion machine and the generator, and wherein, when the expansion machine is in operation, working medium expanded into the exhaust vapor chamber contacts the generator; and means for feeding, in particular injecting, a liquid working medium into the exhaust vapor chamber. The invention also relates to an ORC device comprising the device according to the present invention and to a method for operating the device according to the present invention.

FIELD OF THE INVENTION

The present invention relates to a device comprising an expansionmachine for generating mechanical energy by expanding vapor of a workingmedium; and a generator connected to a shaft of the expansion machineand used for generating electric energy from mechanical energy of theexpansion machine; wherein the expansion machine and the generator forma structural unit with an exhaust vapor chamber between the expansionmachine and the generator. The invention also relates to an ORC systemand a method for operating an expansion machine.

PRIOR ART

An ORC system, i.e. a system for gaining electric energy from heatenergy making use of the Organic Rankine Cycle as a thermodynamic cycle,comprises the following main components: a feed pump conveying theliquid working medium to an evaporator with an increase in pressure, theevaporator itself, in which the working medium is evaporated by additionof heat and, optionally, also superheated, an expansion machine in whichthe highly pressurized vapor is expanded, whereby mechanical energy isgenerated, said mechanical energy being converted into electric energythrough a generator, and a condenser in which the low pressure vaporcoming from the expansion machine is liquefied. From the condenser theliquid working medium is returned to the feed pump of the system via anoptional storage tank (feed tank) and a suction line.

Using modified standard compression machines originating fromair-conditioning and refrigeration technology in ORC systems asexpansion machines is advantageous for various reasons, the motor M ofthe compression machine being then used as a generator G (FIG. 1). Inorder to prevent a possible leakage of the refrigerant to theenvironment, it will be expedient to employ semi-hermetic or hermeticexpansion machines for this case of use. The generator G is here fixedlyintegrated in the housing, whereby the leakage-prone, high-maintenanceshaft feedthrough through the housing of the expansion machine can bedispensed with.

In the case of use as a compressor in the field of air-conditioning andrefrigeration technology, the motor M is used for driving the compressorand the motor is cooled through the cold vapor flowing across the motor(FIG. 1A). In the case of use as an expansion machine in an ORC system,the generator G is therefore exposed to the temperature of the expandedvapor of the working medium, a circumstance that will be unproblematicfor the generator G at exhaust vapor temperatures below 100° C. (FIG.1B).

For increasing the efficiency (higher thermal efficiency) and forextending the field of use, it will, however, be expedient to increasethese vapor temperatures. When the generator G has applied thereto anexhaust vapor temperature exceeding 100° C., this will be problematic asfar as a trouble-free operation is concerned. In this case, the limittemperature for the generator winding may be reached or exceeded (e.g.120° C. in FIG. 1C). Operating the generator and thus the expansionmachine is then no longer possible, or will lead to premature aging orfailure of the insulation of the generator winding. Hence, especiallythe winding temperatures are of decisive importance for the generator.The temperature may be applied to the generator e.g. through thermalconduction in the housing.

Currently used and available expansion machines have operatingtemperatures with limited maximum values. On the one hand, hightemperatures in the expansion machine adversely affect—as describedabove—the near-by generator. As regards this generator, there are limittemperatures which must not be exceeded. On the other hand, theviscosity of the bearing lubricants is problematic, said viscositydecreasing at higher temperatures, whereby bearing lubricationdeteriorates.

In order to still allow the use of waste heat from an ORC process forthe purpose of heating or as process heat, the heat must be given off ona suitable temperature level (60-100° C.). This, however, leads to apoor efficiency of the overall system in the case of low live vaportemperatures. It will therefore be advantageous to counteract thiseffect with higher expansion machine infeed temperatures. However,higher temperatures have the effect that the temperature limits for theuse of the expansion machine will be exceeded (through temperaturelimits for the generator), whereby disadvantages are caused.

DESCRIPTION OF THE INVENTION

It is the object of the invention to overcome the above describeddrawbacks at least partially.

This object is achieved by a device according to claim 1. The deviceaccording to the present invention comprises an expansion machine forgenerating mechanical energy by expanding vapor of a working medium; agenerator connected to the shaft of the expansion machine and used forgenerating electric energy from mechanical energy of the expansionmachine; wherein the expansion machine and the generator form astructural unit with an exhaust vapor chamber between the expansionmachine and the generator, and wherein, when the expansion machine is inoperation, working medium expanded into the exhaust vapor chambercontacts the generator; and means for feeding, in particular injecting,a liquid working medium into the exhaust vapor chamber.

The expanded working medium (exhaust vapor) is cooled by a liquidworking medium downstream of the expansion machine. Due to the infeed,in particular injection into the exhaust vapor chamber, the liquidmedium evaporates upon coming into contact with the hot exhaust vaporand lowers thus the temperature in the expanded medium. The field of useof the volumetric expansion machine is extended, thus allowing theexpansion machine to be used for higher vapor infeed temperatures (e.g.higher than 130° C.). The generator on the expansion machine issufficiently cooled and protected against excessive heating. This alsoleads to an increase in its efficiency. A temperature gradient betweenthe generator and the exhaust vapor of 20 K or more is hereadvantageous, since this will guarantee good cooling of the generator.

The device according to the present invention can be further developedsuch that the means for feeding working medium into the exhaust vaporchamber comprises one or a plurality of openings in a housing of thestructural unit. This provides a possibility of feeding working mediuminto the exhaust vapor chamber.

According to another further development, the shaft may be configured asa hollow shaft and the means for feeding working medium into the exhaustvapor chamber may comprise one or a plurality of openings in said hollowshaft. The working medium fed for the purpose of cooling the exhaustvapor can thus be introduced centrally into the exhaust vapor chamber.

In accordance with another further development, the means for feedingworking medium into the exhaust vapor chamber may comprise one or aplurality of nozzles, which may be arranged in particular at one or aplurality of the openings, the nozzle or nozzles being especiallyconfigured to be controllable. By means of the nozzles, a finedistribution of the working medium fed into the exhaust vapor chamber isaccomplished. The injection or spraying-in leads to a formation ofdroplets, which evaporate in the exhaust vapor chamber partly or fullyand which extract energy from the exhaust vapor due to the evaporationheat thus taken up.

According to another further development, the device according to thepresent invention or one of its further developments may additionallycomprise a turbulence unit for generating a turbulent flow in theexhaust vapor chamber. In this way, a good distribution of the workingmedium fed for the purpose of cooling is accomplished, the exhaust vaporbeing thus cooled more uniformly in space. In addition, a finerdistribution of the working medium in the form of smaller droplets leadsto a faster and more complete evaporation of the liquid working mediumin the exhaust vapor chamber and this also results in better cooling ofthe exhaust vapor.

Another further development consists in that the means for feedingworking medium into the exhaust vapor chamber may comprise a feed linefor liquid working medium leading into the exhaust vapor chamber.

This can be further developed such that the means for feeding workingmedium into the exhaust vapor chamber additionally comprises an orificeor a valve, in particular a controlled or a regulated valve, foradjusting a mass flow of the fed working medium in the feed line.

According to another further development, a temperature sensor may beprovided in the exhaust vapor chamber for measuring the vaportemperature or in the generator for measuring the winding temperature,said temperature sensor being in particular a PTC temperature sensor;and, optionally, a control or regulating unit may be provided forcontrolling or regulating the valve or the orifice, depending on themeasured temperature, in particular for switching the mass flow in thefeed line on and off.

The above-mentioned object is additionally achieved by an ORC device,comprising a device according to the present invention or one of thefurther developments of the latter; a feed pump for pumping liquidworking medium to an evaporator; the evaporator for evaporating theliquid working medium; and a condenser for condensing the vaporousworking medium which exits the structural unit comprising the expansionmachine and the generator.

The ORC device according to the present invention may be furtherdeveloped such that the feed line for liquid working medium leading intothe exhaust vapor chamber is in fluid communication with a line betweenthe feed pump and the evaporator; or the feed line for liquid workingmedium leading into the exhaust vapor chamber is in fluid communicationwith an intermediate space of a multi-stage feed pump; or the feed linefor liquid working medium leading into the exhaust vapor chamber is influid communication with a line between two feed pumps of an arrangementcomprising a plurality of consecutive feed pumps. Due to the tapping ofthe multistage feed pump or tapping between two feed pumps, theadditional expenditure of energy is kept low. Alternatively, the liquidmay be conveyed through a separate pump, which is switched on and off,e.g. in a temperature-dependent manner.

According to another further development, there may be provided anadditional feed line for feeding a lubricating medium to one or aplurality of lubrication points of the expansion machine, and a heatexchanger, in particular a counterflow-type plate heat exchanger, forcooling the lubricating medium with the working medium conducted to theexhaust vapor chamber. Lubrication of the bearings of the expansionmachine is improved by the additional cooling of the lubricant.

The above-mentioned object is additionally achieved by a method foroperating an expansion machine according to claim 12.

The method according to the present invention comprises the followingsteps: generating mechanical energy by expanding vapor of a workingmedium in the expansion machine; generating electric energy frommechanical energy of the expansion machine by a generator connected to ashaft of the expansion machine; wherein the expansion machine and thegenerator form a structural unit with an exhaust vapor chamber betweenthe expansion machine and the generator, and wherein, when the expansionmachine is in operation, working medium expanded into the exhaust vaporchamber contacts the generator; and feeding, in particular injecting,working medium into the exhaust vapor chamber for cooling the expandedvapor.

The method according to the present invention has the advantages thathave already been described in connection with the device according tothe present invention.

The method according to the present invention can be further developedsuch that the further step of adjusting a mass flow of the fed workingmedium can be carried out in a feed line for liquid working mediumleading into the exhaust vapor chamber.

According to another further development, the following additional stepsmay be provided: measuring the vapor temperature in the exhaust vaporchamber; or measuring a winding temperature of the generator; andadjusting the mass flow of the fed working medium by means ofcontrolling or regulating a valve or an orifice in the feed line,depending on the measured temperature, in particular switching the massflow in the feed line on and off.

According to another further development, the following additional stepsmay be provided: feeding a lubricating medium to one or a plurality oflubrication points of the expansion machine; and cooling the lubricatingmedium by the working medium fed to the exhaust vapor chamber.

The above-mentioned further developments may be used separately or theymay be combined with one another in a suitable manner.

Additional features and exemplary embodiments as well as advantages ofthe present invention will be explained in more detail hereinafter withreference to the drawings. It goes without saying that the embodimentsdo not exhaust the scope of the present invention. It also goes withoutsaying that some or all of the features described hereinafter may alsobe combined with one another in other ways.

DRAWINGS

FIG. 1 shows the prior art

FIG. 1A shows a compressor (prior art in air conditioning systems)

FIG. 1B shows an expander (prior art in ORC systems)

FIG. 1C shows an expander (ORC-system development target)

FIG. 2 shows an embodiment of the device according to the presentinvention

FIG. 3 shows a first embodiment of an ORC device according to thepresent invention

FIG. 4 shows a second embodiment of an ORC device according to thepresent invention

FIG. 5 shows a third embodiment of an ORC device according to thepresent invention

EMBODIMENTS

According to the present invention an expanded working medium (exhaustvapor) is cooled by a liquid working medium downstream of the expansionmachine. Through injection into the vapor chamber, the liquid workingmedium evaporates, thus leading to a decrease in temperature in theexpanded working medium. According to a further development, the bearinglubricant is cooled by means of the liquid working medium before it isapplied to the bearing. According to another further development, theworking medium used for the purpose of cooling is tapped off from thecircuit at an appropriate stage of a multi-stage rotary pump.

The field of use of the volumetric expansion machine is extended, thusallowing the expansion machine to be used for higher vapor infeedtemperatures (e.g. substantially higher than 130° C.). The generator atthe expansion machine or at the turbine is sufficiently cooled andprotected against excessive heating. This also leads to an increase inits efficiency. Lubrication of the bearings is improved by theadditional cooling of the lubricating medium. Only a small number of newcomponents is required for realizing this. These new components comprisea connection line for the liquid medium and, in addition, possibly avalve, one or more nozzles and a heat exchanger for the lubricant. Theadditional expenditure of energy is kept low due to the tapping of thefeed pump.

The advantages of the present invention are to be seen in that theoperation of standard expansion machines can be extended; the generatoris protected against excessive heating; the efficiency of the generatoris improved; lubrication of the bearings can be improved; highertemperature levels can be utilized and useful heat from the system canbe given off; no or only a small number of new components will benecessary; and hardly any additional expenditure of energy will berequired.

In particular in semi-hermetic and hermetic screw expansion machines,expanded vapor flows across the generator, which is cooled by saidvapor. At high vapor temperatures (>120° C.), cooling of the generatoris no longer guaranteed. It stands to reason that this effect can becounteracted by cooling the flowing vapor. To this end, a liquid workingmedium is injected into the vapor before the latter comes into contactwith the generator and substantial cooling results from the evaporationenthalpy of said liquid working medium, sensible heat also being takenup to a minor extent. Cooling which utilizes the evaporation enthalpy ismore effective than cooling without phase transition utilizingexclusively the heat capacity. For the working medium R245fa, which isthe current state of the art in ORC systems, as well as for other mediasuitable for higher temperatures, the evaporation enthalpies exceed thespecific heat capacities by a factor of approximately 100.

For use in ORC systems, liquid working medium can be tapped offdownstream of the feed pump and injected into the vapor chamber for thepurpose of cooling the vapor. Injection into the vapor chamber can takeplace through one or a plurality of suitable holes. For betterdistribution of the liquid medium and for faster evaporation due to afine distribution in the form of small droplets, the use of one or of aplurality of nozzles is, however, recommended. In addition, the liquidcooling medium can be introduced in the vapor chamber via a hollow shaftprovided with holes. To this end, it is advisable to use the shaftbetween the expansion machine and the generator. In order to optimizethe distribution, a turbulence unit may be introduced in the vaporchamber. The mass flow required for cooling remains below 10% of thevapor mass flow when the vapor is cooled down by up to 10 K. This massflow can be adjusted via a narrowing cross-section in the cooling line(e.g. via an orifice or a valve). When a nozzle is used for injection,the mass flow can be adjusted through a suitable nozzle.

The way in which the components of the ORC system are interconnectedaccording to the present invention allows higher live-vapor andexhaust-vapor temperatures when standard components are used. Theelevation to a higher temperature level allows the system to be operatedin a combined heat and power (CHP) mode. The heat used for cooling thesystem can thus be used as thermal heat or process heat on a temperaturelevel of approx. 80-100° C. and more.

FIG. 2 shows an embodiment of a device according to the presentinvention. It is a simplified schematic representation (e.g. only onebearing for the shaft is shown). The device according to the presentinvention comprises an expansion machine 110 for generating mechanicalenergy by expanding the vapor of a working medium; a generator 120connected to a shaft 115 of the expansion machine and used forgenerating electric energy from mechanical energy of the expansionmachine; wherein the expansion machine 110 and the generator 120 form astructural unit 100 with an exhaust vapor chamber 140 between theexpansion machine 110 and the generator 120, and wherein, when theexpansion machine is in operation, working medium expanded into theexhaust vapor chamber 140 contacts the generator (by flowing e.g.through intermediate spaces between the stator and the rotor of thegenerator and/or in grooves in the housing of the structural unit 100 inthe area of the generator); and means 150 for feeding, in particularinjecting, a liquid working medium into the exhaust vapor chamber 140,the means 150 according to this embodiment comprising an opening 150 tothe exhaust vapor chamber 140 in the structural unit 100. The workingmedium A enters at a high-pressure-side inlet 111 of the structural unit100 and leaves the structural unit 100 at an outlet 112 as exhaust vaporB or as cooled exhaust vapor B. The shaft 115 is supported on a bearing116 and an access 190 for a bearing lubricant C is provided. The liquidworking medium injected into the opening 150 evaporates at leastpartially thus extracting thermal energy from the exhaust vapor, wherebythe latter is cooled. The resultant temperature is a mixed temperature,which is lower, e.g. by 10-20 K, than the temperature of the exhaustvapor without cooling.

FIG. 3 shows a first embodiment of the ORC device. The ORC devicecomprises a device according to the present invention (e.g. according toFIG. 2) or one of the further developments thereof; a feed pump 130 forpumping liquid working medium to an evaporator (not shown); theevaporator being used for evaporating the liquid working medium from thefeed pump; and a condenser 160 for condensing the vaporous workingmedium which exits the structural unit comprising the expansion machine110 and the generator 120. The means 150 for feeding liquid workingmedium into the exhaust vapor chamber 140 comprises here also a feedline which taps off liquid working medium after the pump (high-pressureside), when seen in the direction of flow, and conducts it into theexhaust vapor chamber 140. The exhaust vapor chamber 140 is only shownschematically in the present and in the following figures andcorresponds to the physical space 140 according to FIG. 2.

FIG. 4 shows a second embodiment of the ORC device. In comparison withthe first embodiment shown in FIG. 3, said second embodimentadditionally comprises a temperature sensor 180 (T) on the generator120, by means of which the winding temperature is measured. Thetemperature sensor 180 may e.g. be a PTC temperature sensor(PTC=Positive Temperature Coefficient, thermistor). In addition, theline 150 has provided therein a switchable or controllable valve 170,which, on the basis of the temperature of the generator measured by thetemperature sensor 180, controls the mass flow of the liquid workingmedium fed into the exhaust vapor chamber 140 for the purpose ofcooling. For example, the valve 170 may be opened (or opened stillwider), when a predetermined temperature limit value is reached orexceeded, whereas otherwise it is not open (or open only to a minorextent). Furthermore, tapping of a multi-stage feed pump 130 between twoneighboring stages of the feed pump 130 is exemplarily carried out inthe case of this embodiment.

FIG. 5 shows a third embodiment of the ORC device according to thepresent invention. In comparison with the first embodiment shown in FIG.3, said third embodiment additionally comprises a cooler 200 for coolinga lubricant fed in a lubricant line 210 to the bearing 116 of theexpansion machine 110 for the purpose of lubrication. The cooler 200 ishere configured as a heat exchanger, in which heat from the lubricant istransferred to liquid working medium, which is fed to the exhaust vaporchamber 140 for the purpose of cooling.

It follows that the benefit of cooling can be increased by cooling, e.g.in a counterflow-type plate heat exchanger, the lubricating medium forthe bearings of the expansion machine, before it enters the bearing,through the liquid working medium used for the purpose of cooling, ifthe lubricant should have a temperature higher than that of the liquidworking medium. When, in addition, the lubricating medium is transferredto the exhaust vapor via the exhaust vapor chamber, also a negativeinfluence of lubricant cooling on the exhaust vapor cooling will beprevented, which negative influence would, in principle, have to beexpected due to the increase in the temperature of the liquid workingmedium used for cooling. In currently used expansion machines, anopening between the bearing housing and the exhaust vapor chamberguarantees that the lubricant is removed from the bearing via theexhaust vapor chamber. The pressure prevailing in the bearing housing issimilar to that on the high-pressure side of the expansion machine.Through the pressure difference between the bearing chamber and thelow-pressure side, the lubricating medium is sucked into the refrigerantvapor and can thus contribute to the cooling of the flowing workingmedium vapor. The heat transferred to the liquid working medium wasextracted from the lubricating medium, so that the temperature of thevapor remains the same, when the exhaust vapor, the lubricating mediumand the liquid working medium have been mixed.

The embodiments shown are only exemplary embodiments and the full scopeof the present invention is defined by the claims.

The invention claimed is:
 1. An Organic Rankine Cycle (ORC) device,comprising: an expansion machine for generating mechanical energy byexpanding vapor of a working medium; a generator connected to a shaft ofthe expansion machine and used for generating electric energy frommechanical energy of the expansion machine; wherein the expansionmachine and the generator form a structural unit with an exhaust vaporchamber between the expansion machine and the generator, and wherein,when the expansion machine is in operation, working medium expanded intothe exhaust vapor chamber contacts the generator; at least one openingfor feeding a liquid working medium into the exhaust vapor chamber forcooling the expanded vapor; an evaporator for evaporating liquid workingmedium; a condenser for condensing vaporous working medium exiting thestructural unit; a feed pump for pumping the condensed liquid workingmedium to the evaporator; and a feed line for liquid working mediumleading into the exhaust vapor chamber and in fluid communication with(i) a line between the feed pump and the evaporator, or (ii) anintermediate space of a multi-stage feed pump; wherein the feed line influid communication with the line between the feed pump and theevaporator is configured to tap off the liquid working medium at a highpressure downstream of the feed pump and upstream of the structural unitformed of the expansion machine and the generator; and wherein the feedline in fluid communication with the intermediate space of themulti-stage feed pump is configured to tap off the liquid working mediumbetween two neighboring stages of the multi-stage feed pump.
 2. The ORCdevice according to claim 1, wherein the structural unit comprises ahousing, and wherein the at least one opening extends through thehousing of the structural unit.
 3. The device according to claim 2,wherein the shaft is configured as a hollow shaft and the at least oneopening comprises one or a plurality of openings in said hollow shaft.4. The ORC device according to claim 1, wherein the shaft is configuredas a hollow shaft and the at least one opening comprises one or aplurality of openings in said hollow shaft.
 5. The device according toclaim 4, further comprising at least one nozzle, which is arranged atone or a plurality of the openings in the hollow shaft, the nozzle ornozzles being configured to control a flow of the liquid working mediuminto the exhaust vapor chamber.
 6. The device according to claim 4,further comprising at least one nozzle, which is arranged at one or aplurality of the openings, the nozzle or nozzles being configured tocontrol a flow of the liquid working medium into the exhaust vaporchamber.
 7. The ORC device according to claim 1, further comprising atleast one nozzle, which is arranged at one or a plurality of theopenings, the nozzle or nozzles being configured to control a flow ofthe liquid working medium into the exhaust vapor chamber.
 8. The ORCdevice according to claim 1, wherein the at least one opening is incommunication with a feed line for feeding the liquid working mediuminto the exhaust vapor chamber.
 9. The ORC device according to claim 8,further comprising a valve, wherein the feed line is in communicationwith the valve for adjusting a mass flow of the fed working medium inthe feed line.
 10. The ORC device according to claim 1, furthercomprising: an additional feed line for feeding a lubricating medium toone or a plurality of lubrication points of the expansion machine; and aheat exchanger for cooling the lubricating medium with the workingmedium conducted to the exhaust vapor chamber.
 11. A method foroperating an expansion machine in an Organic Rankine Cycle (ORC) device,comprising the following steps: generating mechanical energy byexpanding vapor of a working medium in the expansion machine; generatingelectric energy from mechanical energy of the expansion machine by agenerator connected to a shaft of the expansion machine; wherein theexpansion machine and the generator form a structural unit with anexhaust vapor chamber between the expansion machine and the generator,and wherein, when the expansion machine is in operation, working mediumexpanded into the exhaust vapor chamber contacts the generator; feedinga liquid working medium into the exhaust vapor chamber for cooling theexpanded vapor; evaporating liquid working medium by an evaporator inthe ORC device; condensing vaporous working medium exiting thestructural unit by a condenser in the ORC device; and pumping thecondensed liquid working medium to the evaporator by a feed pump in theORC device, wherein feeding the liquid working medium into the exhaustvapor chamber further comprises one of: tapping off liquid workingmedium between the feed pump and the evaporator using a feed line forliquid working medium leading into the exhaust vapor chamber, whereinthe tapping off occurs at a high pressure downstream of the feed pumpand upstream of the structural unit formed of the expansion machine andthe generator; or tapping off liquid working medium between twoneighboring stages of the feed pump using a feed line for liquid workingmedium into the exhaust vapor chamber, wherein the feed pump is amulti-stage feed pump.
 12. The method according to claim 11, comprisingthe further step of: adjusting a mass flow of the fed working medium ina feed line for liquid working medium leading into the exhaust vaporchamber.
 13. The method according to claim 12, comprising the furthersteps of: monitoring at least one selected from the group consisting ofa vapor temperature in the exhaust vapor chamber and a windingtemperature of the generator; and adjusting a mass flow of the fedworking medium by controlling or regulating a narrowing cross-section inthe feed line depending on at least one selected from the groupconsisting of the monitored vapor temperature and winding temperature.14. The method according to claim 11, comprising the additional steps:feeding a lubricating medium to one or a plurality of lubrication pointsof the expansion machine; and cooling the lubricating medium by theworking medium fed to the exhaust vapor chamber.